On the dissociation of I2 by O2(a 1Δ): Pathways involving the excited species I2(A' 3Π2u,A 3Π1u), I2(X 1Σ,υ), and O2(a 1Δ,υ)

Kinetic studies were carried out to explore the role of the excited species I-2(A(') (3)Pi(2u),A (3)Pi(1u)), I-2(X (1)Sigma,upsilon), and O-2(a (1)Delta,upsilon) in the dissociation of I-2 by singlet oxygen. A flow tube apparatus that utilized a chemical singlet oxygen generator was used to measure the I-2 dissociation rate in O-2(a (1)Delta)/I-2 mixtures. Vibrationally excited I-2(X) is thought to be a significant intermediate in the dissociation process. Excitation probabilities (gamma(upsilon)) for population of the upsilon th I-2(X) vibrational level in the reaction I-2(X)+I(P-2(1/2))-> I-2(X,upsilon>10)+I(P-2(3/2)) were estimated based on a comparison of calculated populations with experimentally determined values. Satisfactory agreement with the experimental data [Barnault , J. Phys. IV 1, C7/647 (1991)] was achieved for total excitation probabilities partitioned in two ranges, such that Gamma(25 <=upsilon <= 47)=Sigma(47)(upsilon=25)gamma(upsilon)approximate to 0.1 and Gamma(15 <=upsilon <= 24)=Sigma(24)(upsilon=15)gamma(upsilon)approximate to 0.9. A multipathway I-2 dissociation model was developed in which the intermediates are I-2(A(') (3)Pi(2u),A (3)Pi(1u)) and I-2(X,upsilon). It was shown that the iodine dissociation process passes predominantly through the I-2(A(') (3)Pi(2u),A (3)Pi(1u)) intermediate. These states are populated by collisions of I-2 with vibrationally excited O-2(a (1)Delta,upsilon) at the initiation and the chain stages, when the mole fraction of I-2 is small (eta(I2)< 1%). For higher I-2 concentrations (eta(I2)>= 1%) the excited states are populated in the chain stage by collisions of I-2(X,15 <=upsilon <= 24) with O-2(a (1)Delta).